Refrigeration apparatus

ABSTRACT

A refrigeration circuit comprising a motor-driven compressor, a condenser, an evaporator, and expansion means. The compressor includes an oil reservoir, where a supply of oil is disposed for lubricating the compressor during normal operation thereof. Associated with the compressor is a heating element, operable to heat the oil when the compressor is inoperable. A safety switch prevents the compressor from becoming energized if the heating element has not functioned while the compressor was inoperable.

United States Patent David N. Shaw Liverpool, N.Y. 829,417

June 2, 1969 May 4, 1971 Carrier Corporation Syracuse, N.Y.

Inventor Appl. No. Filed Patented Assignee REFRIGERATION APPARATUS 2Claims, 2 Drawing Figs.

US. Cl. 62/84,

62/230, 62/192, 62/468 Int. Cl. F25b 43/02 Field of Search 62/192, 193,84, 468, 469, 230

[56] References Cited I UNITED STATES PATENTS 2,107,887 2/1938 Davenport62/193 3,133,429 5/1964 Griffin 62/469 3,208,237 9/1965 Gerteis 62/843,377,816 4/1968 Beryer 68/192 Primary Examiner-William J. WyeAttorneys-Harry G. Martin, Jr. and J. Raymond Curtin ABSTRACT: Arefrigeration circuit comprising a motordriven compressor, a condenser,an evaporator, and expansion means. The compressor includes an oilreservoir, where a supply of oil is disposed for lubricating thecompressor during normal operation thereof. Associated with thecompressor is a heating element, operable to heat the oil when thecompressor is inoperable. A safety switch prevents the compressor frombecoming energized if the heating element has not functioned while thecompressor was inoperable.

REFRIGERATION APPARATUS BACKGROUND OF THE INVENTION This inventionrelates to a refrigeration circuit, and more particularly torefrigeration circuits including motor-driven compressors.

It is well known that under certain conditions, some refrigerants andoil used as a lubricant for the motor compressor unit are freelymiscible. During normal operation of the refrigeration circuit, becauseof operating pressures and temperatures, the oil in the sump of acompressor will be substantially free of refrigerant. However, onshutdown when the circuit reaches ambient temperature and the pressureequalizes within the circuit, the refrigerant vapor and oil in the sumpof the compressor will mix to form a substantially homogenous solution.

This phenomenon is not localized, and it is possible that the entireliquid refrigerant charge within the circuit may be absorbed by the oilcharge in the sump. When the ambient temperature at the compressor sumpapproaches the evaporator temperature, liquid refrigerant will boil offin the evaporator and will condense in the compressor sump and therebygo into solution with the oil.

Upon startup of the compressor, the oil sump which is usually a part ofthe crankcase of the compressor drops to suction pressure and thecompressor mechanism may agitate the solution. The combination of thedrop in suction pressure and possible mechanical agitation causes-therefrigerant in solution to attempt to return to its vapor state. Sincethe refrigerant at shutdown is in a substantially homogenous solution,the flashing of admixed liquid refrigerant to vapor may carry therewitha substantial amount of the oil charge and may even result in the entiresolution turning into a foam.

Foaming of the oil will materially increase the amount of oil carriedover into the refrigerant discharge line. Foaming may become so severethat all the oil is pumped out of the sump. Not only will this leave thecompressor without lubrication, which may produce bearing failure in ashort period of operation, but there is also the possibility thatnoncompressible slugs of liquid refrigerant and oil will enter thecompressor cylinders and cause serious damage to the compressor in theform of broken valves and pistons and bent or broken rods and shafts.

To avoid the problem of crankcase oil dilution, crankcase heaters aregenerally employed. On shutdown of the compressor, temperaturethroughout the inactive refrigeration unit eventually equalizes with theprevailing ambient temperature, with the exception of the compressorcrankcase which is suitably heated, a satisfactory temperature beingapproximately 40 F. to 60 F. above ambient temperature. At thistemperature, a small amount of refrigerant will be absorbed by the oilcharge; however, this mixture of oil and refrigerant will have asufficient vapor pressure to discourage further refrigerant from passinginto the vapor state and being absorbed into the crankcase solution.

The crankcase heater may be an electrical resistance element. Theresistance element may either be installed directly in the crankcase, indirect contact with the oil, or may be wrapped around the outer surfaceof the compressor casing in heat transfer relation with the oil storedin the crankcase.

If the heating element were to become inoperable due to burning out,becoming disconnected, or the like, while the compressor was inoperable,the problem sought to be overcome may return upon startup of thecompressor.

Therefore, the object of this invention is a control operable to preventthe compressor from starting up if the crankcase heater has failed.

SUMMARY OF THE INVENTION The novel control herein disclosed is utilizedwith refrigeration circuits having refrigerant compressors employingcrank case heaters.

The primary purpose of the crankcase heater as explained heretofore, isto maintain the oil at a sufficiently warm temperature to minimizeabsorption of refrigerant during shutdown of the refrigeration circuit.However, in applications where costs to operate the heating element arerelatively low when compared to manufacturing costs of installingcomponents to automatically cycle the heating element in response to thecycle of the refrigeration circuit, the heating element may be operableat all times without introducing any problems. If the operating costsare higher than the installation costs, then the additional componentsrequired to cycle the heating element will be installed. In either case,the refrigeration control herein disclosed will prevent the compressorfrom becoming operable if the crankcase-heating'element has failedduring the shutdown period of the refrigeration unit.

The control includes a relay disposed in the circuit supplying power tothe heating element. The relay controls the position of a normally openswitch disposed in the circuit controlling the energization' of thecompressor.

Assume the refrigeration circuit is employed in an application where itis preferable to operate the crankcase-heating element only when therefrigeration circuit is inoperable. If the crankcase heater has notfunctioned during the shutdown period, for example, the element may haveburnt out, the relay in the element control circuit will be deenergized.With the relay inoperable, the switch controlled thereby is in itsnormally open position and thus prevents the compressor from becomingoperable.

A bypass arrangement or holding circuit prevents the switch fromdeenergizing the compressor, once the refrigeration unit is operable andthe heating element is inoperable.

Alternatively, if the crankcase-heating element is always operable, thenormally open switch in the compressor control circuit may be openedduring compressor operation or during shutdown, by the failure of theheater and the concurrent deenergization of the relay controlling theswitch.

If the compressor stops during a period of time when it should beoperating, or if the compressor fails to start, the operator will thentrouble-shoot to determine the problem and will then be able to repairthe crankcase heater before the serious problems previously noted occur.To expedite the trouble-shooting" operation, indicator lights may beinstalled.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates schematically atype of refrigeration apparatus to which the present invention applies,and a wiring diagram of a preferred form of the refrigeration circuitcontrol serving as the subject of the invention; and

FIG. 2 illustrates an alternative embodiment of the invention of thispatent.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, andin particular to FIG. 1, there is schematically shown anair-conditioning system employing a refrigeration circuit embodying theinvention herein disclosed.

The refrigeration circuit or unit disclosed is representative of acircuit utilized in window mounted room air conditioners. Therefrigeration unit includes an outdoor heat exchange coil or condenser10. The condenser 10 is connected by means of line 11 with the dischargeside of a suitable refrigerant compression mechanism, for example, areciprocating-type compressor 12. The gaseous refrigerant produced incompressor 12 subsequently flows through condenser 10 and is condensedby ambient air routed over the surface of the condenser by outdoor fan13. Liquid refrigerant formed in the condenser 10, flows through line14, thermal expansion valve 15 and line 16 to indoor coil or evaporator17. It is understood other suitable expansion devices, as a capillarytube, may be employed in lieu of expansion valve 15. The thermalexpansion valve 15 in conjunction with the compressor 12 separates therefrigeration unit into a high-pressure side and a low-pressure side.

Liquid refrigerant in evaporator 17 is converted to vaporous refrigerantas it extracts heat from the medium, for example, room air passed overits surface by indoor fan 18. The cooled air is thereafter passed to thearea being conditioned by suitable means, such as grilles or vents (notshown). Vaporous refrigerant from coil 17 flows via suction line 19 tocompressor 12 to complete the refrigerant flow cycle.

The compressor 12 includes a crankcase 20 which functions as a reservoiror sump for storing a supply of oil for lubricating the various parts ofthe compressor during normal operation. Associated with the compressor12 is heating element 21, shown as a resistance coil. The heatingelement 21 may be disposed directly in the crankcase of the compressormay be wrapped around the outer surface of the casing of the compressorin heat transfer relation with the oil stored in the sump. The heatingelement 21 is utilized to prevent the problems discussed hereinabove.

Again referring to FIG. 1, a preferred form of the control circuit forthe refrigeration unit hereinabove described is schematically shown. Asuitable source of electrical power is represented by lines L and I.connected to a primary winding 24 of a transformer 23. It is understoodthat a polyphase source of electrical power may be employed if thecircuit is suitably modified.

As is apparent from referring to FIG. 1, the heating element 21 isdirectly connected to the source of electrical power. Thus, heatingelement 21 is operable at all times when a source of electrical power isavailable. Connected in series with heating element 21 is relay 22controlling the operation of normally open switch 26. The purpose ofrelay 22 and switch 26 will be described more fully hereinafter.

The secondary winding of the transformer 23 is connected in series witha switch 27, responsive to the temperature of air circulating in thearea being served by the equipment. When switch 27 is closed, current issupplied to control relay 28. Energization of relay 28 closes normallyopen switch 29. Connected in series with switch 29 are normally closedswitches 31 and 32. Normally closed switches 31 and 32 are safetydevices, respectively a high-pressure cutout and a motor overloadcutout. Other safety devices known to the art, such as a low-pressurecutout and a low oil pressure cutout, may also be used. The occurrenceof the condition protected against will open the particular switch,thereby either preventing the refrigeration unit from becoming operableor stopping the unit during the normal operation thereof.

Assuming switches 31 and 32 are in their normally closed position andrelay 22 has closed switch 26, relay is then energized. Energization ofrelay 30 will close normally open switches 33 and 34. Closure of switch33 actuates fan motor 35, operating fans 13 and 18. Closure of switch 34connects compressor motor 36 across lines I. and L thereby starting thecompressor 12.

As heretofore explained, heating element 21 is used to warm thelubricating oil stored in the crankcase 20 of the compressor duringshutdown periods of the refrigeration unit. As shown in FIG. 1, theheating element 21 may also be energized during the operating time ofthe unit without introducing any problems. Heating element 21 will beused continuously in applications where the initial costs of addingcomponents to the compressor to automatically deenergize the heatingelement 21 in response to the refrigeration cycle are relatively largewhen compared to the costs involved in operating the heating elementduring operation of the unit. The heating element will maintain the oilat a relatively warm temperature during shutdown of the unit to minimizeabsorption of the refrigerant, and to thereby prevent the concomitantproblems discussed heretofore.

If the heating element were to burn out, become disconnected, or tootherwise become inoperative during the unit shutdown period, relay 22will then be deenergized. Deenergization of relay 22 will place switch26 in its normally open position, thereby preventing energization ofrelay 30. With relay 30 deenergized, switch 34 will be maintained in itsnormally open position, thereby preventing the compressor motor frombecoming operable as desired.

Referring now to FIG. 2, there is disclosed a modified embodiment of theinvention. In particular, the heating element 21 is inoperable duringoperation of the refrigeration unit. The circuit schematicallyrepresented by FIG. 2 may be particularly useful in applications wherethe cost of operating the element 21 is relatively high when compared tothe cost of installing components to automatically deenergize theelement 21 when the refrigeration unit is in operation.

Connected in series with heating element 21 and relay 22 is normallyclosed switch 41, the position thereof being controlled by relay 30.Relay 30 additionally controls the position of normally open switch 37.The closure of the latter switch will establish a bypass or holdingcircuit through lines 38 and 39 around normally open switch 40. Thereason for the bypass circuit will be explained more fully hereinafter.

In lieu of switch 26, relay 22 now controls the position of normallyopen switch 40. Switch 40 has a sufficiently delayed opening afterdeenergization of relay 22 for a reason that will be explainedhereinafter.

Assume heating element 21 has been operable during the units shutdownperiod, and thermally responsive switch 27 now senses the area beingserved requires cooling and closes.

As noted hereinabove, closure of switch 27 will energize relay 28thereby closing switch 29. Since we have assumed heating element 21 hasbeen operable, relay 22 is therefore energized and switch 40 is closed.With switches 29 and 40 in their closed positions, relay 30 is thenenergized, thereby closing switches 33, 34, and 37 and opening switch41. The opening of switch 41 will deenergize relay 22 and heatingelement 21. In addition, switch 40 is also opened when relay 22 isdeenergized. However, the opening of switch 40 at this time will notprevent operation of the unit, since the time delay provided for theopening of the latter switch will have allowed switch 37 to be closed,thereby creating the bypass or holding circuit through lines 38 and 39about the switch 40.

In case the heating element had failed to function during the unitsshutdown, deenergization of relay 22 will have opened switch 40, thuspreventing energization of the compressor motor 36 as desired.

The control circuit hereinabove discussed will prevent compressorfailure and costly repairs in case the crankcase heater has notfunctioned in the designed manner.

While I have described and illustrated a preferred embodiment of myinvention, it will be understood that my invention is not limitedthereto, since it may be otherwise embodied within the scope of thefollowing claims.

I claim:

1. A control for a refrigeration circuit including a motordrivencompressor, a condenser, an evaporator, and expansron means, comprising:

A. a supply circuit for providing electrical energy to said compressormotor including a controller including a first switch for connectingsaid motor to said supply circuit, said controller further including anenergizing coil;

B. a lubricant reservoir in said compressor having a supply of thelubricant disposed therein for lubricating said compressor;

C. heating means associated with said compressor, operable to heat saidlubricant; and

D. switch means operable to prevent said compressor motor from beingconnected to said supply circuit if said heating means has beeninoperable while said compressor motor has been deenergized.

2. A method of operating a refrigeration system including a motor-drivencompressor, a condenser, an evaporator and expansion means, saidcompressor having an oil reservoir with oil disposed therein forlubricating said compressor, said compressor further having heatingmeans associated therewith, operable to warm said oil, comprising thesteps of:

compressor is deenergized; and

D. preventing the compressor from becoming operable in response to apredetermined condition; if said heating means has been inoperable whilesaid compressor has been deenergized.

1. A control for a refrigeration circuit including a motordriven compressor, a condenser, an evaporator, and expansion means, comprising: A. a supply circuit for providing electrical energy to said compressor motor including a controller including a first switch for connecting said motor to said supply circuit, said controller further including an energizing coil; B. a lubricant reservoir in said compressor having a supply of the lubricant disposed therein for lubricating said compressor; C. heating means associated with said compressor, operable to heat said lubricant; and D. switch means operable to prevent said compressor motor from being connected to said supply circuit if said heating means has been inoperable while said compressor motor has been deenergized.
 2. A method of operating a refrigeration system including a motor-driven compressor, a condenser, an evaporator and expansion means, said compressor having an oil reservoir with oil disposed therein for lubricating said compressor, said compressor further having heating means associated therewith, operable to warm said oil, comprising the steps of: A. circulating a refrigerant through said refrigeration system by energization of said compressor, in response to a predetermined thermal condition; B. terminating the operation of said refrigeration system upon satisfaction of a predetermined thermal condition; C. operating said heating means to warm said oil while said compressor is deenergized; and D. preventing the compressor from becoming operable in response to a predetermined condition, if said heating means has been inoperable while said compressor has been deenergized. 